Concealed slide fastener

ABSTRACT

The invention relates to a sliding clasp fastener of the concealed element type comprising series of coupling elements which are, on one side each, sewn on a carrier tape and consist of a thermo-plastics filament wound in the form of a modified helix, as well as carrier tape, which is folded back on itself on the side which is remote from the series of coupling elements.

[54] CONCEALED SLIDE FASTENER 3,343,234 9/1967 Chery 24 205.1 c 3,149,388 9/1964 Wilcken.... 24/205,l C [76] Invent flans'umch D 5408 Nassau 3,484,906 12/1969 Yoshida 24/20s.1 c Lab", schubflchweg Hans 3,490,110 1/1970 Frohlich 24/205.l6 c Waffenschred, G y 3,609,827 10/1971 Heimberger 24/205.1 c [22] Filed: Nov. 1, 1971' FOREIGN PATENTS OR APPLICATIONS 2 App]. 194 145 1,292,429 9/1969 Germany 24/205.

1,128,413 9/1968 Great Britain Related US. Application Data 6,604,611 10/1966 Netherlands Division of 1 7 16 97 Pat N 273,471 6/1967 Sweden 24/205 3,665,879.

Primary Examiner-Bemard A. Gelak [30] F i A li ti P i it D t Attorney, Agent, or Firm-Friedman & Goodman Feb. 18, 1969 Germany P 19 08 068.3 Feb. 18, 1969 Germany P 19 08 069.4 [57] v ABSTRACT The invention relates to a sliding clasp fastener of the [52] US. Cl. .....'24/205.1 C, 24/205. 16 C concealed element type comprising series of coupling [51] Int. Cl A441: 19/12 elements which are, on one side each, sewn on a car- [58] Field of Search"; ..24/205.1 C, 205.16 C, rier tape and consist of a thermo-plastics filament 205,13 C wound in the form of a modified helix, as well as carrier tape, which is folded back on itself on the side [56] References Cited which is remote from the series of coupling elements. U D STATES PATENTS 8 Claims, 9 Drawing Figures 3,430,304 3/1969 Swainson 24/205.1 C

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INVENTOR HANS-ULRICH SOUR BY MM QHQWZM ATTORNEY S CONCEALED SLIDE FASTENER This is a division, of application Ser. No. 1 1,617 filed Feb. 16, 1970, now US. Pat. No. 3,665,879.

The invention relates also to a method of making fasteners of the said type.Sliding clasp fasteners of the concealed element type per se are well known. The problem involved with this type of sliding clasp fastener is that the coupling head portions of the series of coupling elements should be fastened as close as possible to the fold of the tape and that the interengaged head portions should be prevented from being exposed when the finished sliding clasp fastener is subject to transverse pull. British Pat. No. 1 120 935 for example, discloses a sliding claspfastener of the concealed element type where the problem of fastening the coupling head portions of the series of coupling elements as close as possible to the edge of the carrier tape is solved by putting the head portions between the weft threads in a zone without warp threads of the carrier tape, and laying the edge of the tape, which does have warp threads on the other side of the coupling elements and fastening it there preferably by sewing. For this purpose the various well known shapes of coupling elements (oval shape, dumbbell shape (FIG. 8), meander shape and the like) are used. The disclosed type of sliding clasp fastener, however, cannot be termed a sliding clasp fastener the series of coupling elements of which is sewn to the tape on one'side only.

So far this requirement of concealing the series of coupling elements has been met rather imperfectly and strictly speaking the fasteners of the so-called concelaed element type do not deserve this name, at least as far as those which are made of thermo-plastics filament are concerned.

Furthermore, the prior art comprises sliding clasp fasteners of the aforementioned type with a helical filament enclosing a cord, namely a so-called filler cord, which at least partially fills the inside cross-section of the series of coupling elements and, additionally, has the function of a connecting element between the sewing thread joining the cord to the carrier tape and the series of coupling elements. As indicated by the term filler cord" the cord should fill the inside cross-section of the series of coupling elements, namely to prevent the lines of stitching from being distorted by transverse pull exerted on the finished sliding clasp fastener. Further it is well known and common practice to fasten the sliding clasp fasteners of the so-called concealed element type of the kind mentioned above as different from fasteners of the non-concealed element type by at least two lines of stitching per series of coupling elements to the carrier tape (see British Pat. No. 1 128 413 and 1 073 424 and Swedish Pat. No. 213 471 and 214 277).

Surprisingly it was found that the second line of stitching is no longer required, if also the filler cord is omitted. A consideration, which might lead to an explanation of this advantageous and surprising effect may be that a filler cord itself is not sufficiently rigid but flexible so that, possibly, the filler cord contributes only a little to the rigidity of the individual coupling element. Thus the coupling element which has to be big to accommodate the filler cord would be unstable in itself and the filler cord would not improve this instability though it was expected to do so.

For a sliding clasp fastener of the concealed element type comprising series of coupling elements which are,

on one side each, sewn on a carrier tape and consist of a thermo-plastics filament wound in the form of a modified helix, as well as carrier tape which is folded back on itself on the side which is remote from the series of coupling elements it is suggested according to the invention to sew each series of coupling elements by a single line of stitching to the tape without using any filler cord.

Pursuing the course taken by this measure and the possibilities disclosed it is suggested that the series of coupling elements without filler cord be made smaller, in particular that the inside cross-section be made smaller than it could be done as long as a filler cord was used. Preferably the passage between adjacent coupling elements for receiving the sewing thread and the needle handling the thread is so dimensioned in the direction of its larger cross-section in regard to size and shape of this cross-section that the thermo-plastics filament to be used for making the series of coupling elements can no longer be put through this passage or can just i.e. without play be put through the passage. Thus the thermo-plastics filament*(+ to be used is not the filament), which might be obtained from a finished series ofcoupling elements or a finished sliding clasp fastener, i.e. the filament which has passed all stages of production, but the unworked filament as taken from the reel supplied by the manufactures for being processed to a series of coupling elements. The needle passages of the sliding clasp fastener ready for use should be dimensioned so as to accommodate such unworked filament without play or not to accommodate it at all.

According to another feature of the invention the space, which does not contain any filler cord has definite dimensions, namely the maximum inside width measured perpendicular to the carrier tape plane of the space without any filler cord between the legs of a coupling element under consideration equals approximately half the diameter of the circular cross-section filament to be used for making the series of coupling elements. A sliding clasp fastener of the concealed element type dimensioned according to this rule has particularly advantageous strength properties.

According to a specific embodiment of the invention the coupling elements of the series of coupling elements have the so-called dumb-bell shape (for example according to FIG. 8 of British Pat. No. l 935), i.e. looking in the direction of the sliding clasp fastener axis of symmetry the coupling head and coupling foot portions of each coupling element are wider than the legs or central portions linking them. Preferably the seam if looked at from the center of a coupling element is located closer to the head portion than to the foot portion.

Particular advantages, first of all in regard to fineness and strength, could be obtained, if the sewing thread were merely sunk into the filament surface and part of the filament material were simply displaced; this could be achieved by a heat treatment known per se which would be performed after sewing. The inserting of a sewing thread into a notch provided in the surface of the filament constituting the sliding clasp fastener is known per se, but the notch is formed by removal of part of the filament material and this must inevitably lead to weakening of the filament and a notch effect. If, on the other hand, the sewing thread is sunk into the filament surface, i.e., if material displacement effected instead of material removal, the notch effect and weakening of the filament are eliminated,since the filament volume remains unaffected. Also in regard to production this process is considerably less complicated because the sewing thread sinks itself into the filament, i.e., measures to ensure that the sewing thread moves exactly into the notch previously provided in the filament are no longer required.

Thus the invention relates further to a method of making a sliding clasp fastener of the concealed element type with series of coupling elements consisting of a plastics filament wound in the form of a modified helix and on one side each sewn on one carrier tape each in such a way that the coupling head portions of the coupling elements are remote from the tape edge which is adjacent to the portion of the tape, which supports the series of coupling elements, and that after the sewing stage, the wider portion of the tape which does not support the series of coupling elements is folded back on the line of stitching along a line which is near the coupling head portions.

This method, which is preferably provided and adapted for making a sliding clasp fastener of the concealed type and sewn by one line of stitching and without any filler cord, is characterized according to the invention by the common application of the following steps:

a. Prior the sewing, the series of coupling elements is allowed to set as much as is required for withstanding, without damage the mechanical stress which will result from subsequent treatment, and possible heating is so limited that the temperature remains below the setting temperature of the series of coupling elements and that a noticeable change in shape, in particular of the filament length-tothickness ratio, can be made within this temperature range below the setting temperature;

b. the series of coupling elements are then interengaged and c. sewn on the carrier tapes while the tape portions to be folded back on the line of stitching are guided between the needles; I

d. the series of coupling elements sewn on the tapes are subsequently heated to a temperature near their softening temperature in a manner known per se.

Individual steps of this procedure are prior art, partially also in combination with other claims. Thus it was disclosed earlier that series of coupling elements of the type described above can first be interengaged by pairs and only then be sewn on the tape. The inclusion of this we-ll known step of procedure into a procedure for making a sliding clasp fastener of the concealed element type is only made reasonably applicable by the special way of guiding of the carrier tapes according to c) of the invention. The new procedure permits to reduce the costs of production of such sliding clasp fastener of the concealed element type and to make finer (less clumsy) fasteners; this is of special interest to the clothing industry.

The special heat treatment known per se permits to change the filament diameter-to-length ratio in order to improve the strength of the connection between filament and carrier tape. According to another feature of the invention the sewing machine needles operate parallel to each other, but they need not operate at a right angle to the plane formed by the carrier tape portions supporting the coupling elements at the point of sewing, if it is assumed that the tape portions are plane and rigid at the point of sewing. During the sewing process the portion of the tape held and guided between the needles forms, in fact, a right angle with this plane.

As it is usual with fasteners of the non-concealed element type, the series of coupling elements may be fed into the sewing machine below the carrier tape supporting it if a double chain stitch seam is made so that in case of the fastener of the concealed element type, the needles operate from their point of stitching parallel to the tape portions to be folded later on, then first pierce the tape portion supporting the series of coupling elements and finally the passages between the coupling elements.

In this way the gripper thread chain is laid on the series of coupling elements.

It it is intended to utilize the double chain stitch seam to improve the positioning of the seam near the coupling head portions substantially, the series of coupling elements is fed into the sewing machine above the carrier tape so that the needles first pierce the passages between the coupling elements and thereafter the tape portions supporting the coupling elements the longer tape portions, which are to be folded later on are guided between the needles, which have already done the stitching. By feeding the material into the sewing machine this way the gripper thread chain is laid on the tape portions supporting the series of coupling elements, and since the gripper thread chain is a sort of head it will produce a blunt folding edge of the longer tape portions and improve the covering of the coupling head portions as well as the positioning of the seam when the finished fastener will be subject to transverse stress.

A particularly good product is obtained by the method according to the invention, if series of coupling elements are used the legs of which joining the head and foot portions are recessed or intended from the head and foot portions. Preferably this recess or indentation is located closer to the coupling head portion than to the coupling foot portion so that the seam which lies on the rear head portion, so-to-speak on the back of the head, is located particularly close to the point where the coupling element engages its counterelement. In addition or for this purpose the foot portion may be provided with a bulge exceeding that of the head portion so that the foot portion is thicker or, related to the tape plane, higher than the head portion. The seam may be laid into a step previously provided in the filament for this purpose or prepared during the heat treatment. This is achieved preferably by making the filament and the thread of materials of different softening temperatures so that the filament moves into the thread or the thread into the filament when the material of the lower softening point yields. Preferably the materials are so selected that the filament softens first and the thread moves into the filament material.

This feature of the method can, in general, be applied to the manufacture of sliding clasp fasteners in that all the elements forming the sliding clasp fastener for example, filament for the series of coupling elements, sewing thread and carrier tape) are caused to move into each other by appropriate heat treatment, i.e., the temperature applied is slightly below the melting temperature of one of the thermoplastic materials.

Furthermore it is intended to use threads consisting of a plastics core and cotton covering instead of cotton sewing threads or pure synthetic sewing threads. If according to the invention the temperature applied to the suggested thread is such that the plastics core shrinks like va synthetic sewing thread, it adheres very closely to the legs of the coupling elements, and during the dyeing process later on the cotton covering can have the same shade as the carrier tape, if it also consists of cotton.

If however, plastics carrier tapes are used, the step of the procedure mentioned above provides at the same time a pleat effect since the tapes are fixed in the final planeposition they will have in the garment. So far such pleat effect could not be obtained without a special aftertreatment of conventional cotton tapes and also of plastics tapes.

According to the invention sliding clasp fasteners consisting of synthetics only can be dyed all over and fast with good penetration if the thermo-setting temperature is utilized. Also individual plastics components of the sliding clasp fastener can be dyed according to this method.

According to the invention the concealing of the coupling elements by the supporting carrier tapes is also ensured by the fact that on each coupling element the distance betwen the coupling surface and the seam may be very short in relation to the total width of the individual coupling element, that the seam can no longer be drawn towards the foot portions by transverse pull and that the legs can thus no longer be exposed.

Additional features of the invented clasp fastener and of two possible realisations of the invented method will result from the following specification and from the claims. In the specification reference will be made to the accompanying drawing where:

FIG. I is a section through one half of a sliding clasp fastener according to the invention, regarded in the direction of the fastener axis;

FIG. 2 is a plan view of two interengaged finished series of coupling elements without carrier tape of a sliding clasp fastener according to the invention; the view being taken perpendicular of the fastener and carrier tape planes as indicated by arrow ll in FIG. ll;

FIG. 3 is a view of another embodiment of the invention corresponding to FIG. ll;

FIG. 4 is a cross-section merely through the carrier tape of the fastener according to FIG. 3 where the tape, however, is shown in the folded condition;

FIG. 5 is a view of another embodiment of the invention corresponding to FIG. ll;

FIG. 6 is an enlarged detail lateral view of the part of the plastics filament leg where the sewing thread is sunk into the filament surface;

FIG. 7 is a perspective view of the arrangement of the two carrier tapes in respect to each other,of the series of coupling elements and the needles during the sewing stage;

FIG. 8 shows an alternative method of feeding the materials to be sewn into the sewing machine, and

FIG. 9 shows a preferable design of a coupling element out of the series of coupling elements made of a continuous filament, with the preferable location of the seam and the folded carrier tape looking in the direction of the longitudinal axis of symmetry of the sliding clasp fastener.

As compared with an actual sliding clasp fastener, FIG. I shows a considerably enlarged half of such fastener. Also in regard to the ratio of coupling element size and filament thickness FIG. l is not according to scale.

Approximately at lltl there is the axis of symmetry of the sliding clasp fastener. The coupling element shown comprises the coupling head portion 12, the coupling foot portion Ml, and the legs 16 and 1%. The external contour of the element is that of a dumb-bell, i.e., foot and head portions of the element are higher than the central portion or legs connecting them. The useful cross-section without filler cord is indicated by numeral 20. According to the invention, the clear height of said cross-section should equal approximately half the diameter of the unworked filament used.

The series of coupling elements is so sewn on the carrier tape 22 that the coupling head portions 12 are remote from edge 24 of the tape which limits tape portion 26 supporting the series of coupling elements and is adjacent to the head portions. The remaining portion of carrier tape 22 is folded back on itself, namely on portion as supporting the series of coupling elements. Thus a fold is obtained at 28; in the ideal case of the concealed element type fastener this fold is only half the coupling head portion depth away from the front of all coupling head portions. The sewing thread 32 of the single line of stitching lid is located so deep in the fila ment forming the coupling elements that the filament covers the thread entirely or almost entirely. This special feature permits to make the concealed element type fastener still more graceful and finer.

FIG. 2 shows the needle passage 11 (shaded) which is located between two adjacent coupling elements 15 and 17 of a series of coupling elements 19 which was interengaged with its counter-series 21. What really matters according to the invention is the maximum cross-section of the needle passage, which is not necessarily in the direction perpendicular to the carrier tape plane; in the example shown, the passage of maximum cross-section will rather be slightly inclined from the left to the right, as determined by the direction of the leg incoming at a coupling head portion and the leg outgoing there. In the case of series 19 shown in FIG. 2, the leg incoming from the left is the upper leg and the outgoing leg is the lower leg, and since they do not lie exactly on top of eachother but diverge substantially right from the coupling head portion, the needle passage of maximum cross-section is located between the upper legs slightly more to the left than between the lower legs. Thus it passes from the left top to the right bottom. This passage should be so narrow that the unworked filament which has not been subject to any forming process or heat treatment can, at most, be put through the passage without play. The passage, however, can still be narrower so that the unworked filament cannot be put therethrough. It should be noted, however, that in all cases the needle passage of the finished sliding clasp fastener sewn to the garment or the like is meant. In order to test this feature in practice, the series of coupling elements, preferably interengaged with its counter-series, should be detached from the sliding clasp fastener which is ready for sale and it should be attempted to put the unworked filament through the needle passages.

For a filament of circular cross-section the relationship between the needle passage of the finished fastener and the unworlted filament 113 is as shown in FIG. 2.

Shape and diameter of the unworked filament may be different from the cross-section of the finished filament, as shown at 130.

According to FIG. 3 the tape is reinforced at the fold between tape portions 26 and 22; the reinforcements improve the positioning of the fold at the head portion. As shown in detail in FIG. 4 a reinforcement by warp threads or films or the like is provided at 35 and at 36 plastics material or the like is woven in to reinforce the sewing thread area. Thus the tape fold possesses considerable inherent strength, and this also improves the strength of the sliding clasp fastener.

The embodiment of the invention according to FIG. 3 furthermore shows a head portion 12 a, which is lower than the foot portion 14a. The line of stitching consists of an upper thread 32 which is not sunk into the filament surface and a lower thread chain 34. The recessed legs 16 and 18 are also located in front of plane 33.

According to another advantageous embodiment of the invention and with the use of reinforced carrier tapes and the common use of chain stitch seams an additional improvement is obtained by not arranging the lower thread chain, as usual, on the coupling element series and the upper or needle thread at the carrier tape, but by arranging them in the reverse manner so that the lower thread chain, i.e., the gripper thread, which is bulkier lies below portion 26 of the carrier tape. Thus the tape reinforcement applied makes the finished fastener more resistant to transverse pull. This arrangement facilitates sinking of the less rising or bulky upper thread into the plastics filament by heat and facilitates easier sliding of the slider over the plastics coupling element surface which is no longer dis turbed by elevations caused by the thread. The slide does no longer need an internal profile which would otherwise be required with a view to the lower thread chain.

FIG. shows a series of coupling elements of symmetrical design with a thread arranged at the center of the leg. The upper thread is embedded in the filament without reduction of the filament volume but only with displacement of filament material. The displacement of filament material is indicated at 31. When transverse pull is exerted on portion 22 of the carrier tape, the tape reinforcement is supported by the lower thread chain 34.

Another advantageous feature consists in that, if cotton carrier tapes are used, a synthetic filler may be woven into the tape in the area of the needle stitches. The filler should be selected so that it will set during the heat treatment which will be performed in a manner known per se, and additionally fix the sewing thread in the weave of the carrier tape. If plastics carrier tapes are used, the filler may consist of a material, which sets at lower temperatures and earlier than the carrier tape itself.

FIG. 7 shows in a simplified manner, in profile and not in entire length the carrier tapes 110 and 112 which are so fed into the sewing machine that portions 114 and 115 of each tape supporting the coupling elements are perpendicular to the remaining tape portions 116 and 118. Edges 120 and 122 will later be the external edges of the finished fastener with its coupling elements in the interengaged state. Prior to sewing, the series of coupling elements 124 and 125 are interengaged by their coupling head portions (arrow 126) and together fed into the sewing machine in the direction of arrows 128 and 130. The sewing needles 132 and 134 are arranged parallel to each other; needle 134 cannot be seen becasue of the perspective view and is indicated by a broken line. Carrier tapes and 112 are guided through the machine between the needles in the direction of arrow 136. The needles operating parallel to each other and to' the planes of tape portions 116 and 118 need not operate perpendicular to tape portions 114 and 115, they may operate at another angle thereto. The direction of the forward and backward movements of the needles is indicated by the double arrow 138.

FIG. 8 shows an alternative method of feeding the materials to be sewn and arranging the sewing thread.

According to FIG. 8 the interengaged series of coupling elements 124 and are so fed into the sewing machine that they lie plane on tape portions 114 and 115, whereas tape portions 116 and 118 are arranged perpendicular to portions 114 and 115. The needles 132 and 134 (FIG. 8) operate and move in the same direction as shown in FIG. 7, i.e., parallel to the planes of tape portions 116 and 118 and at the same time at a right angle or at another angle to tape portions 114 and 1 15. In FIG. 8, however, the needles are on the side of the tape portions 114 and 115, which also support the coupling element series; preferably the series of coupling elements and the needles are provided above and tape portions 116 and 118 below the tape portions 114 and 115. With this arrangement the gripper chain threads 117 and 119 will be located in the fold between tape portions 114 and 116 and 115 and 118 respectively.

FIG. 9 shows the convenient arrangement of seam joining the coupling elements to the carrier tape. The individual coupling element has the preferably dum-bell shape; in the form shown in FIG. 9 dimension 12 which is the width of the foot portion exceeds dimension a, the width of the head portion 142. The arrangement of the seam between the narrowest portion approximately at the center of the element and the widest portion 144 of the coupling head portion per se need not be applied together with the other feature shown, namely the wider foot portion 146. In general, it is sufficient to apply either of the two features.

In FIG. 9 the tape portions 115 and 118 are shown in their final position, i.e., in the folded state.

In case of doubt all features described and/or shown herein shall be considered essential to the invention individually or in any reasonable combination.

I claim:

1. A sliding clasp fastener of concealed element type including two series of coupling elements arranged for engagement with each other, characterized in each series of coupling elements comprising:

a thermoplastic filament disposed in a modified helical arrangement to define said coupling elements, each coupling element including a coupling head portion and a foot portion,

Upper and lower central leg portions disposed between and connecting each head portion respectively to associated foot portions, said head and foot portions being wider between their respective upper and lower surfaces than the width between upper surface of said upper leg portion and lower surface of said lower leg portion to define a dumbbell configuration,

a tape including a first portion folded back on a second portion to define a fold therebetween,

said lower surfaces of said head and foot portions being positioned against an upper surface of said tape second portion, a free edge of said tape second portion being disposed adjacent to said lower surface of each foot portion, said fold being disposed adjacent to said lower surface of each head portion to conceal said sliding clasp fastener when in a closed position,

only one single line of stiches connecting said coupling elements to said tape second portion without any filler cord,

said single line of stitches being disposed in a groove in each of said upper surfaces of said head portions, and

said single line of stitches having a sewing thread thickness substantially equal to the width of said groove in each of said upper surfaces of said head portions.

2. A sliding clasp fastener according to claim 1, wherein a maximum inner space between upper and lower elements of said filament is approximatelyhalf the diameter of the circular cross-section of said filament to increase stability of said coupling elements, whereby necessity of a filler cord in said inner space at said single line of stitches is eliminated.

3. A sliding clasp fastener according to claim 2, wherein said upper and lower elements of said filament are part of said head portions respectively.

4. A sliding clasp fastener according to claim 1, wherein said single line of stitches is closer to said fold than to said free edge of said tape with said single line of stitches being disposed on said head portions 5. A sliding clasp fastener according to claim 1, wherein depth of said head portion groove is greater than sewing thread thickness of said single line of stitches whereby sewing thread is disposed below said upper surfaces of said head portions.

6. A sliding clasp fastener according to claim 1, wherein the width between said upper and lower surfaces of said foot portions is greater than the width between said upper and lower surfaces of said head portions.

7. A sliding clasp fastener according to claim 1, wherein a lower thread chain of said single line of stitches is disposed between said first and second portions of said tape.

8. A sliding clasp fastener according to claim 1, wherein passage between adjacent coupling elements for accommodating sewing thread of said single line of stitches and the needle handling said sewing thread is dimensioned in direction of its larger cross-section in regard to size and shape of this cross-section that said thermoplastic filament used for making said series of coupling elements can be put through said passage without play. 

1. A sliding clasp fastener of concealed element type including two series of coupling elements arranged for engagement with each other, characterized in each series of coupling elements comprising: a thermoplastic filament disposed in a modified helical arrangement to define said coupling elements, each coupling element including a coupling head portion and a foot portion, Upper and lower central leg portions disposed between and connecting each head portion respectively to associated foot portions, said head and foot portions being wider between their respective upper and lower surfaces than the width between upper surface of said upper leg portion and lower surface of said lower leg portion to define a dumb-bell configuration, a tape including a first portion folded back on a second portion to define a fold therebetween, said lower surfaces of said head and foot portions being positioned against an upper surface of said tape second portion, a free edge of said tape second portion being disposed adjacent to said lower surface of each foot portion, said fold being disposed adjacent to said lower surface of each head portion to conceal said sliding clasp fastener when in a closed position, only one single line of stiches connecting said coupling elements to said tape second portion without any filler cord, said single line of stitches being disposed in a groove in each of said upper surfaces of said head portions, and said single line of stitches having a sewing thread thickness substantially equal to the width of said groove in each of said upper surfaces of said head portions.
 2. A sliding clasp fastener according to claim 1, wherein a maximum inner space between upper and lower elements of said filament is approximately half the diameter of the circular cross-section of said filament to increase stability of said coupling elements, whereby necessity of a filler cord in said inner space at said single line of stitches is eliminated.
 3. A sliding clasp fastener according to claim 2, wherein said upper and lower elements of said filament are part of said head portions respectively.
 4. A sliding clasp fastener according to claim 1, wherein said single line of stitches is closer to said fold than to said free edge of said tape with said single line of stitches being disposed on said head portions.
 5. A sliding clasp fastener according to claim 1, wherein depth of said head portion groove is greater than sewing thread thickness of said single line of stitches whereby sewing thread is disposed below said upper surfaces of said head portions.
 6. A sliding clasp fastener according to claim 1, wherein the width between said upper and lower surfaces of said foot portions is greater than the width between said upper and lower surfaces of said head portions.
 7. A sliding clasp fastener according to claim 1, wherein a lower thread chain of said single line of stitches is disposed between said first and second portions of said tape.
 8. A sliding clasp fastener according to claim 1, wherein passage between adjacent coupling elements for accommodating sewing thread of said single line of stitches and the needle handling said sewing thread is dimensioned in direction of its larger cross-section in regard to size and shape of this cross-section that said thermoplastic filament used for making said series of coupling elements can be put through said passage without play. 